The present invention is related to vacuum tubes and more particularly to vacuum tube grid structures.
Conventional high power vacuum tubes often use a tungsten matrix cathode which usually takes the form of a porous tungsten cylinder filled with barium oxide, aluminum oxide and calcium oxide. Although this type of cathode has many advantages, under some circumstances the cathode tends to emit a considerable amount of barium and barium oxide which becomes deposited on the tube grids. Only the deposited barium oxide remains on the grids causing them to emit electrons thus rendering the tube unusable. To solve the problem of the grid emission, a variety of coatings such as titanium and zirconium have been applied to the grids in an effort to reduce or eliminate the electron emission. However, these relatively short life coatings have met with little success.